This invention relates to a method and a kit for determining the biocide concentration in a liquid containing a biocide of the type which liberates formaldehyde in water, especially under acid conditions.
A good example of one field where the invention is particularly useful is that of detecting the biocide concentration in a liquid coolant-lubricant of the type used for rolling sheet metal or forming cylinders from sheet metal, to which certain biocides have been added. Microorganisms, including both bacteria and fungi, are generally present in all such coolants involving water solutions or water emulsions of mineral-oil based compositions or synthetic lubricants. Unless the growth rate of these microorganisms is carefully controlled, the productive coolant life can be shortened considerably; replacing the coolants usually results in excessively high maintenance costs. Therefore, it is good practice to add a suitable biocide to the coolant. As long as the biocide is active, the coolant is preserved from attack by microorganisms.
The problems have been to determine whether the biocide is within the right concentration range after the biocide-containing coolant has been in use for some time. To do this it is necessary to determine the concentration of the biocide. The biocidal ability of the fluid may be exhausted or it may still be present. If present, it is not only wasteful to add more of the biocide, but it also may lead to poisoning the environment. Overuse of the biocide is quite undesirable, but underuse also has serious consequences.
It has been found that some of the most useful biocides break down in water, and especially in acid solutions, to liberate formaldehyde, which appears to be in proportion to the biocidal potentiality of the biocide. In fact, it may well be that liberation of formaldehyde is the biocidal activity of some or all of these biocides.
For example, one biocide is 1-(3-chloroallyl)-3,5,7 -triaza-1-azoniaadamantane chloride. This material, and some others like it (such as hexahydro 1,3,5-triethyl-S-triazine and hexahydro 1,3,5-tris-(2-hydroxyethyl)-S-triazine), break down to yield a number of compounds including, ultimately, water, ammonia, carbon dioxide, and chlorine. However, the intermediate degradation yields formaldehyde in a mole-to-mole ratio, as well as some amines, amine formates, hexamethylenetetramine methyl chloride and hexamethylenetetramine hydrochloride. Of these compositions, formaldehyde is easily detected by a procedure which I have developed.
Coolants and cutting oils with such biocides can be tested for formaldehyde liberation, but when the coolant or cutting oil is an oil-in-water emulsion it is too opaque for testing color intensity in a simple colorimeter. The same is true for testing latex paints containing biocides. Moreover, even though the test (without a colorimeter) can be rather straightforward when such coolants are fresh, problems arise when they have been in use for a while. The reading of color intensity by any method is then made inaccurate by the presence of a grayish cast in the coolant, which is apparently due to non-filterable metallic fines that become associated with oil droplets, or perhaps are in a free state within the coolant. The amount of grayness in even the same coolant varies from customer to customer and from time to time, with the amount and conditions of use of the coolant. I have discovered that this problem can be overcome by the development of a two-phase breaking and clearing solution, which leads to especially good results.